About This Presentation
May 15, 2021. This thesis summary video is provided courtesy of Zahir Barahmand.
Zahir Barahmand, Energy and Environmental Engineering, University of South-Eastern Norway
Chandana Ratnayake, USN-SINTEF
Chameera Jayarathna, SINTEF Industry
Aluminum is now the world’s second most used metal. Since aluminum has a unique combination of appealing properties and functionalities, it allows for significant energy savings in many applications, such as vehicles and buildings. Although this energy-saving leads to lower CO2 emissions, the production process of aluminum still dramatically impacts the environment. The process used almost exclusively in the aluminum industry is the Hall-Héroult process with a considerable amount of carbon footprint with high energy consumption. As the best alternative, Alcoa’s process (which is not industrialized yet) is based on the chlorination of processed aluminum oxide, reducing the traditional method’s negative impacts.
In continuation of Alcoa’s effort, the present study aims to investigate the possibility of a new sustainable and low-carbon aluminum production process by designing an industrial fluidized bed reactor equipped with an external (due to high corrosion inside the reactor) gas-solid separation unit to handle a total of 0.6 kg/s of solid reactants and produce aluminum chloride as the main product. The research focuses on determining the best bed height based on the available reaction rates, determining the best reactor dimension to reduce particle outflow under isothermal conditions (700°C), and optimization of the reactor to achieve minimum channeling in the bed, enhancing the hydrodynamics through Computational Particle Fluid Dynamic (CPFD) simulations using commercial software; Barracuda Virtual Reactor®. The optimization stage includes changes in the reactor geometry, fluid inflow pattern, and distribution system.
The relevant process is an exothermic reaction in a fluidized bed reactor, where solid alumina reacts with chlorine and carbon monoxide and produces aluminum chloride as the main product of the process, besides carbon dioxide can be separated. The previous studies have assumed an isothermal condition at 700℃, which is the optimum temperature for this reaction. The reactor’s temperature has been kept in the range of 650-850℃ (most preferably 700℃) because below that temperature range, the reaction rate drops and above that range, the alumina (which usually is γ-alumina) will be transferred to θ-alumina and α-alumina phases which is not desirable for the purpose.
Based on previous simulation studies (isothermal), the CPFD method has been utilized to thermal study and simulate the overall heat transfer of the system, including convective fluid to the wall, fluid to particle, and radiation heat transfer. By comparing the thermal results from Barracuda®, it is found that the needed total heat duty transferred to the environment agrees well with the Gibbs reactor simulation in Aspen Plus® (~ 1.62 MW). Radial and axial heat transfer coefficient profiles at different levels show that almost all the heat has been transferred in the lower half of the reactor, making the design more challenging. At the steady-state, the range for the fluid temperature inside the reactor has been recorded 700-780℃.
In the present study, Autodesk Inventor®, Barracuda®, and Aspen Plus® are used for 3D modeling of the reactor, CPFD simulation for multiphase (solid-gas) reaction, and process simulation for validating the CPFD results, respectively.